Culture medium

ABSTRACT

A culture medium is used for culturing neural cells. Each neural cell includes a neural cell body and at least one neurite branched from the neural cell body. The culture medium includes a substrate and a carbon nanotube structure located on the substrate. The carbon nanotube structure includes a number of carbon nanotube wires spaced apart from each other. A distance between adjacent carbon nanotube wires is greater than or equal to diameters of the neural cell bodies. The carbon nanotube wires are capable of guiding extending directions of the neurites.

RELATED APPLICATIONS

This application claims all benefits accruing under 35 U.S.C. §119 fromChina Patent Application No. 201110217845.2, filed on Aug. 1, 2011 inthe China Intellectual Property Office, the disclosure of which isincorporated herein by reference.

BACKGROUND

1. Technical Field

The present disclosure relates to a culture medium.

2. Discussion of Related Art

Many people suffer from neurological disorders as a result of neuroninjuries. Neural grafting can provide relief from these injuries. Neuralgrafting is a surgical transfer of tissue from various sources intospecific areas of the nervous system that have been affected by injury.The neural grafting serves as a “bridge” to connect the proximateinjured neurons. Grafted cells may synthesize and releasegrowth-promoting factors near the injured neurons, thereby promotingneuron regeneration.

What is needed, therefore, is to provide a culture medium used toculture neural cells employed in the wound, for prompt healing.

BRIEF DESCRIPTION OF THE DRAWINGS

Many aspects of the embodiments can be better understood with referencesto the following drawings. The components in the drawings are notnecessarily drawn to scale, the emphasis instead being placed uponclearly illustrating the principles of the embodiments. Moreover, in thedrawings, like reference numerals designate corresponding partsthroughout the several views.

FIG. 1 is an isometric view of one embodiment of a culture medium.

FIG. 2 is a transmission electron microscope (TEM) image of oneembodiment of a carbon nanotube film.

FIG. 3 is a TEM image of one embodiment of stacked carbon nanotubefilms.

FIG. 4 is an optical microscopy image of one embodiment of neuronsstained with fluorescence, wherein the neurons are cultured by using theculture medium shown in FIG. 1.

FIG. 5 is a flow chart of one embodiment of a method for making aculture medium.

FIG. 6 is a scanning electron microscope (SEM) image of one embodimentof a drawn carbon nanotube film.

FIG. 7 is an SEM image of one embodiment of stacked carbon nanotubefilms.

FIG. 8 is a flow chart of one embodiment of a method for growing neuronsusing the culture medium shown in FIG. 1.

FIG. 9 is an isometric view of one embodiment of a culture medium.

FIG. 10 is an optical microscopy image of one embodiment of neuronsstained with fluorescence, wherein the neurons are cultured by using theculture medium shown in FIG. 9.

FIG. 11 is an isometric view of one embodiment of a culture medium.

FIG. 12 is an isometric view of one embodiment of a neural graft using aculture medium.

DETAILED DESCRIPTION

The disclosure is illustrated by way of example and not by way oflimitation in the figures of the accompanying drawings in which likereferences indicate similar elements. It should be noted that referencesto “an” or “one” embodiment in this disclosure are not necessarily tothe same embodiment, and such references mean at least one.

FIG. 1, illustrates one embodiment of a culture medium 10 used toculture neural cells. Each neural cell includes a neural cell body andat least one neurite branched from the neural cell body. The culturemedium 10 includes a carbon nanotube structure 12 and a substrate 14.The carbon nanotube structure 12 is located on and makes contact withthe substrate 14 by van der Waals force.

The carbon nanotube structure 12 includes a plurality of carbonnanotubes orderly arranged. The term ‘orderly’ describes the carbonnanotubes being arranged in a consistently systematic manner, e.g., thecarbon nanotubes are arranged approximately along a same direction andor have two or more sections within each of which the carbon nanotubesare arranged approximately along a same direction (different sectionscan have different directions). In one embodiment, the carbon nanotubestructure 12 consists of a plurality of carbon nanotubes orderlyarranged. The carbon nanotube structure 12 can be a “free-standing”structure having carbon nanotubes joined with each other by van derWaals force. That is, the carbon nanotube structure 12 can retain aspecific shape without any support because of the van der Waals forcebetween adjacent carbon nanotubes. In addition, the carbon nanotubestructure 12 connected by van der Waals attractive force can bend easilywithout breaking. Thus, the carbon nanotube structure 12 can have goodelasticity and ductility, thereby allowing the carbon nanotube structure12 to be tailored and employed to cure a wound having any shape.

The carbon nanotube structure 12 can be patterned by including a numberof carbon nanotube wires 123 spaced from or crossed with each other. Adiameter of each carbon nanotube wire 123 can range from about 1micrometer to about 10 micrometers. A distance between two adjacentcarbon nanotube wires 123 can be equal to or larger than a diameter ofthe neural cell body. In one embodiment, the distance between twoadjacent carbon nanotube wires 123 ranges from about 20 micrometers toabout 100 micrometers. If the carbon nanotube wires 123 in the carbonnanotube structure 12 are crossed, the carbon nanotube wires 123 candefine a number of pores. An effective diameter of each pore is equal toor larger than the diameter of the neural cell body. In one embodiment,the effective diameter of each pore ranges from about 20 micrometers toabout 100 micrometers.

In one embodiment, the distance between two adjacent carbon nanotubewires 123 or the effective diameter of each pore is equal to or largerthan the diameter of the neural cell body. The neurons are grown on theculture medium 10, and the neuron cells will be absorbed on the surfaceof the substrate 14. The carbon nanotube wires 123 can guide growingdirections of the neurites. The neurites can grow along the carbonnanotube wires 123. Thus, the arrangement of the carbon nanotube wires,the distance between adjacent carbon nanotube wires, or the effectivediameter of pores in the carbon nanotube structure 12 can be arranged toform a patterned carbon nanotube structure 12. The patterned carbonnanotube structure 12 can control the growing directions of the neuritessuch that the neurons can be grown oriented in any desired direction.

The carbon nanotube wire 123 includes a number of carbon nanotubesorderly arranged. The carbon nanotube wire 123 can include the carbonnanotubes joined end to end by van der Waals force. The carbon nanotubesin the carbon nanotube wire 123 can be substantially oriented along asame direction or spirally arranged along the axial direction of thecarbon nanotube wire 123.

The carbon nanotube structure 12 can be a free standing film. The carbonnanotube structure 12 can include at least one carbon nanotube film.Referring to FIG. 2, the carbon nanotube film can include a number ofcarbon nanotube wires juxtaposed and separated from each other. At leastone carbon nanotube in the carbon nanotube film is located betweenadjacent carbon nanotube wires and combines with the adjacent carbonnanotube wires by van der Waals force. The carbon nanotube wires in thecarbon nanotube film are substantially arranged along a singledirection. The carbon nanotube film can be a free standing structure bycombining adjacent carbon nanotube wires with the at least one carbonnanotube. In one embodiment, a number of carbon nanotubes are joinedwith two adjacent carbon nanotube wires by van der Waals force. In oneembodiment, each carbon nanotube wire consists of carbon nanotubesjoined end to end along the axial direction of the carbon nanotube wire.

In one embodiment, the carbon nanotube structure 12 includes a number ofstacked carbon nanotube films shown in FIG. 3. Adjacent carbon nanotubefilms in the carbon nanotube structure 12 are combined by van der Waalsforce, and the carbon nanotube wires in two adjacent carbon nanotubefilms defines angles along the axial direction of the carbon nanotubewires. The angles can be larger than or equal to 0 degrees, and lessthan or equal to 90 degrees.

A surface of the carbon nanotube structure 12 can be polarized to apolar surface, during a process of culturing neuronal cells using theculture medium 10. The carbon nanotubes in the surface of the carbonnanotube structure 12 are polarized. Charges on the surface of thecarbon nanotube structure 12 are changed after the surface of the carbonnanotube structure 12 is formed into the polar surface. Surface chargepolarities of the carbon nanotubes in the polar surface of the carbonnanotube structure 12 are opposite to surface charge polarities of theneural cells. As such, the surface charge polarities of the carbonnanotubes in the polar surface and the surface charge polarities of theneural cells attract each other. The surface charge polarities of thecarbon nanotubes in the polar surface and the surface charge polaritiesof the neural cells can have attractive forces between them. Therefore,the surface charge of the polar surface is different from that of theneural cells, and the neural cells can be absorbed on the polar surface.

The carbon nanotube structure 12 is electrically conductive, thermallyconductive, and acoustical, due to the excellent electricalconductivity, thermal conductivity, and acoustic property of the carbonnanotubes. The neuronal cells can be grown by stimulation fromelectricity, heat, or phonation. Therefore, the neuronal cells are grownorderly on the culture medium 10, which is beneficial for researchingthe effect of electricity, heat, or phonation on the neuronal cells.

The substrate 14 can be used to lay or support the carbon nanotubestructure 12 and the pre-cultured neuronal cells. The shape, material,and thickness of the substrate 14 can be selected as desired. In oneembodiment, the shape of the substrate 14 is substantially the same asthat of the carbon nanotube structure 12, and the carbon nanotubestructure 12 completely covers a surface of the substrate 14. Thesubstrate 14 can be a planar structure or a curved structure, such asquadrate sheet-shaped structure, arc-shaped structure, steppedstructure.

The material of the substrate 14 can be a biocompatible material. Thebiocompatible material can be a biodegradable material, non-biotoxicmaterial, or carbon nanotube sheet-shaped material. For example, thebiodegradable material can be thermoplastic starch, polylactide,polyvinyl alcohol, or aliphatic polyesters. The non-biotoxic materialcan be silicone. The carbon nanotube sheet-shaped material consists ofcarbon nanotubes. The carbon nanotube sheet-shaped material has afree-standing property and a certain mechanical strength, such as acarbon nanotube film or a carbon nanotube net structure. The substrate14 can be flexible, such as silicone or a carbon nanotube material. Assuch, the culture medium 10 can be also flexible.

In other embodiments, the material of the substrate 14 can be anon-biocompatible material. The non-biocompatible material can beplastic, such as polystyrene. The substrate 14 can be a plastic culturevessel, a plastic watch glass, or a plastic sheet-shaped structure. Ifthe substrate is a plastic culture vessel or a plastic watch glass, theculture medium 10 can be stored directly as culture cells without theneed of another container to load the culture medium 10 and the cells.

In one embodiment, the substrate is made of a biocompatible material.The culture medium 10 can be transplanted into a biological body andform a shape as desired. The shape and the thickness of the culturemedium 10 can be designed as a shape and thickness of a wound on thebiological body. If the culture medium 10 is transplanted into thewound, the neuronal cells close to the wound can regenerate tore-communicate with and re-connect to each other, thus the wound can berehabilitated. If the thickness of the carbon nanotube structure 12 isthin, the mechanical strength of the carbon nanotube structure 12 willbe small, and the surface area of the carbon nanotube will be large. Thecarbon nanotube structure 12 can be easily broken by an outer force andeasily adhere to other objects. Thus, the carbon nanotube structure 12will not be easily broken and can avoid adhering to hydrophilic objectsbecause the carbon nanotube structure 12 is located on the substrate 14.The carbon nanotube structure 12 fixed on the substrate 14 can be easyto transfer.

In one embodiment, the culture medium 10 consists of a circular andsheet-shaped plastic substrate and a carbon nanotube structureconsisting of a single carbon nanotube film. The carbon nanotube filmincludes a number of carbon nanotube wires 123 extending substantiallyalong a same direction and separated from each other. The carbonnanotube wires 123 are substantially parallel to each other. At leastone carbon nanotube is combined with and connects the two adjacentcarbon nanotube wires 123. The distance between the two adjacent carbonnanotube wires is larger than or equal to 30 micrometers, and less thanor equal to 60 micrometers. Each carbon nanotube wire 123 includes anumber of carbon nanotubes substantially oriented along the extendingdirection of the carbon nanotube wire 123. Thus, if the neuronal cellsare cultured on the culture medium 10, the neuronal cells are absorbedon the surface of the circular and sheet-shaped plastic substrate.Neurites differentiated from the neuronal cells shown in FIG. 4 aresubstantially linearly grown along the axial direction of the carbonnanotube wires 123.

Referring to FIG. 5, if the carbon nanotube wires in the carbon nanotubestructure 12 are spaced from each other, one embodiment of a method formaking the culture medium 10 includes:

S110, providing an original carbon nanotube structure including at leastone drawn carbon nanotube film including a number of carbon nanotubesjoined end to end by van der Waals force and substantially orientedalong a same direction;

S120, forming the carbon nanotube structure 12 including the spacedcarbon nanotube wires 123 from the original carbon nanotube structure;and

S130, fixing the carbon nanotube structure 12 on the substrate 14.

In step S110, the drawn carbon nanotube film is a free-standingstructure consisting of carbon nanotubes. Referring to FIG. 6, the drawncarbon nanotube film includes a plurality of carbon nanotubes that canbe arranged substantially parallel to a surface of the drawn carbonnanotube film. A large number of the carbon nanotubes in the drawncarbon nanotube film can be oriented along a preferred orientation,meaning that a large number of the carbon nanotubes in the drawn carbonnanotube film are arranged substantially along a single direction. Inthe drawn carbon nanotube film, an end of one carbon nanotube is joinedto another end of an adjacent carbon nanotube arranged substantiallyalong the same direction by van der Waals attractive force. A smallnumber of the carbon nanotubes are randomly arranged in the drawn carbonnanotube film, and has a small if not negligible effect on the largernumber of the carbon nanotubes in the drawn carbon nanotube filmarranged substantially along the same direction. The carbon nanotubesoriented substantially along the same direction may not be perfectlyaligned in a straight line, and some curve portions may exist. Somecarbon nanotubes located substantially side by side in contact with eachother cannot be excluded.

In one embodiment, the original carbon nanotube structure includes anumber of stacked drawn carbon nanotube films as shown in FIG. 7.Adjacent drawn carbon nanotube films can be adhered by only the van derWaals attractive force therebetween.

An angle can exist between the carbon nanotubes in adjacent drawn carbonnanotube films. The angle between the aligned directions of the adjacentdrawn carbon nanotube films can be in a range from about 0 degrees toabout 90 degrees. In one embodiment, the angle between the aligneddirections of the adjacent drawn carbon nanotube films is about 90degrees. Simultaneously, aligned directions of adjacent drawn carbonnanotube films can be substantially perpendicular to each other, thus aplurality of micropores and nodes can be defined by the original carbonnanotube structure.

The drawn carbon nanotube film can be made by the following steps:providing a carbon nanotube array; and drawing the carbon nanotube filmfrom the carbon nanotube array.

The step S120 can include the following steps:

S121, suspending the original carbon nanotube structure; and

S122, treating the suspended original carbon nanotube structure using asolvent to form the carbon nanotube structure 12 including a number ofcarbon nanotube wires 123.

In step S121, the original carbon nanotube structure can be suspended byfixing two opposite sides of the original carbon nanotube structure. Inone embodiment, most of the carbon nanotubes extend substantially alonga single direction, the two opposite sides of the original carbonnanotube structure are substantially perpendicular to the extendingdirection of the carbon nanotubes, and the two opposite sides of theoriginal carbon nanotube structure are fixed. In one embodiment, theoriginal carbon nanotube structure is a single drawn carbon nanotubefilm drawn from a carbon nanotube array.

In step S122, after the original carbon nanotube structures are treatedwith solvent, juxtaposed carbon nanotubes in the original carbonnanotube structure will shrink, and the carbon nanotubes joinedend-to-end substantially along a same direction will converge intoparallel carbon nanotube wires. Thus, the carbon nanotube structure 12is formed.

The step S122 can include the following steps: atomizing the solventinto a number of liquid drops, the diameters of the liquid drops beingless than or equal to 10 micrometers; spraying the liquid drops into thesurface of the original structure by a flowing gas to soak the originalcarbon nanotube structure; and evaporating the solvent in the originalstructure, so that under a surface tension of the soaked original carbonnanotube structure, the adjacent and parallel carbon nanotubes in thedrawn carbon nanotube film converge and join end-to-end by van der Waalsforce to form a number of carbon nanotube wires juxtaposed and spacedfrom each other, thereby forming the carbon nanotube structure 12.

The solvent can be atomized by gas atomization, ultrasonic atomization,or adding aerosol. The solvent can be alcohol, methanol, acetone, aceticacid, water, or other volatile materials. In one embodiment, the solventis alcohol. During the process of atomizing the solvent, the airpressure should be small, and the original carbon nanotube structureshould not be broken. The carbon nanotube wires 123 in the carbonnanotube structure 12 are used to guide the neurites growing along thecarbon nanotube wires 123. It is noted that there are a number of carbonnanotubes located between adjacent carbon nanotube wires 123 andcombined with the adjacent carbon nanotube wires 123. The carbonnanotube structure 12 can be made by treating the original carbonnanotube structure, so the method for making the culture medium 10 iseasy.

In one embodiment, the carbon nanotubes in the original carbon nanotubestructure are substantially oriented along the same direction. Step S120can be executed by applying a force substantially perpendicular to theaxial direction of the carbon nanotubes in the original carbon nanotubestructure. For example, the step S120 can further include the followingsteps:

providing at least one elastic supporter, such as a spring, elasticrubber, or rubber ring;

suspending the original carbon nanotube structure, the original carbonnanotube structure being at least partly fixing on the at least oneelastic supporter; and

drawing the at least one elastic supporter along an elastic drawingdirection, to change distances between juxtaposed carbon nanotubes inthe original carbon nanotube structure, wherein the elastic drawingdirection is substantially perpendicular to the extending direction ofthe carbon nanotubes in the original carbon nanotube structure. Thus,the distances between juxtaposed carbon nanotubes can be increased orreduced.

In step S130, the carbon nanotube structure 12 is placed on a surface ofthe substrate 14. The carbon nanotube structure 12 is soaked by anorganic solvent. The organic solvent in the carbon nanotube structure 12is evaporated such that the carbon nanotube structure 12 is fixed on thesurface of the substrate 14 by van der Waals force, because of thereduction of the surface tension of the carbon nanotube structure 12.The carbon nanotube structure 12 can be soaked by dropping or sprayingthe organic solvent on the surface of the substrate 14. The organicsolvent can be the same as the solvent in step S122, such as alcohol,methanol, acetone, acetic acid, or other solvent which can beevaporated.

The method for making the culture medium 10 can also include: providingthe carbon nanotube structure 12 including the carbon nanotube wires123; and fixing the carbon nanotube structure 12 by treating the carbonnanotube structure 12 using the organic solvent. In one embodiment, thecarbon nanotube wires 123 are untwisted carbon nanotube wires, which aredirectly drawn from a carbon nanotube array. In another embodiment, thecarbon nanotube wires 123 are twisted carbon nanotube wires, which aremade by twisting the untwisted carbon nanotube wires or a carbonnanotube film structure. The twisted carbon nanotube wire includes aplurality of carbon nanotubes substantially spiraling along an axialdirection of the twisted carbon nanotube wire. The carbon nanotubestructure 12 can be formed by locating the twisted or untwisted carbonnanotube wires side by side, or weaving the twisted or untwisted carbonnanotube wires.

Referring to FIG. 8, one embodiment of a method for culturing neuralcells using the culture medium 10 can include:

Step A, providing the culture medium including a substrate and a carbonnanotube structure located on the substrate, the carbon nanotubestructure including at least one carbon nanotube film including a numberof carbon nanotube wires spaced apart from each other or crossed witheach other;

Step B, forming a polar surface in the carbon nanotube structure bytreating the carbon nanotube structure; and

Step C, culturing the neural cells on the polar surface to grow neuritesalong the carbon nanotube wires.

One purpose of step B is to change the surface charge polarity of carbonnanotubes in a surface of the carbon nanotube structure. Thus, thepolarized carbon nanotube structure can absorb and be biologicallycompatible with neural cells for neural cells adherent growth.“Compatible” in the text means the carbon nanotube structure and theneural cells can coexist. Step B can include the following steps:

B1, sterilizing the culture medium; and

B2, treating the carbon nanotube structure in the sterilized culturemedium using a poly-D-lysine solution or polyetherimide solution.

In step B1, the culture medium can be sterilized by irradiating orheating, and the carbon nanotube structure is sterilized by ultravioletlight irradiating or heating. The method for sterilizing the culturemedium is not limited, as long as the carbon nanotube structure issterilized.

In step B2, the poly-D-lysine solution or polyetherimide solution isdropped onto the surface of the carbon nanotube structure, until thepoly-D-lysine solution or polyetherimide solution covers the surface ofthe carbon nanotube structure. The surface of the carbon nanotubestructure is covered with the poly-D-lysine solution or polyetherimidesolution for more than 10 hours or until the surface of the carbonnanotube structure is polarized. The surface charge polarity of thepolar surface of the carbon nanotube structure is different from thesurface charge polarities of neural cells. The neural cells can betightly absorbed on the polar surface. The polar surface of the carbonnanotube structure can provide a location for culturing the neuralcells. The poly-D-lysine solution or polyetherimide solution covered onthe carbon nanotube structure is rinsed using sterilized deionized waterto reduce and prevent the poly-D-lysine solution or polyetherimidesolution affecting the neural cells.

The carbon nanotube structure can be treated with the poly-D-lysinesolution or polyetherimide solution to change the surface charge andform the polar surface. As such, it is unnecessary to treat the carbonnanotube structure with plating methods, coating methods, or chemicalmodifications, so that the carbon nanotube can absorb the neural cells.Therefore, the method for culturing neural cells is easy.

In one embodiment, the substrate in the culture medium is a sheet-shapedstructure. The culture medium can be located in a container, such as aplastic culture vessel, or a plastic watch glass, to culture the neuralcells. Thus, step B includes the sub-steps of: providing the container,and placing the culture medium in the container, the substratecontacting with the bottom surface of the container; sterilizing thecontainer and the culture medium; and treating the culture medium withthe poly-D-lysine solution or polyetherimide solution.

Step C can include sub-steps of:

C1, seeding a number of neuron cells on the polar surface of the carbonnanotube structure; and

C2, growing the neuron cells seeded on the polar surface.

In step C1, a neuron solution is dropped onto the polar surface untilthe neuron solution completely covers the polar surface. The neuronsolution is formed by dispersing a number of neuron cells into aplanting solution. The neuron cells in the neuron solution are notdifferentiation cells, meaning the cells are in the original state ornot mature, thus the neurites may not branch from the cells or thelengths of neurites are short. Therefore, the neuron cells seeded on thecarbon nanotube structure are not branched neuron cells. The neurons canbe mammalian neuron cells, such as hippocampal neuron cells.

In step C2, the neurons on the culture medium are incubated in anincubator with a CO₂ concentration of about 5% and a temperature ofabout 37° C. During the optimal culture period, under guiding of thecarbon nanotube wires in the carbon nanotube structure, a plurality ofneurites from a cell body of the individual neuron cells will branchalong the axial directions of the carbon nanotube wires and connect withadjacent neurons to form a neuronal network. Thus, the neurites can begrown in any desired direction or orientation. That is, the extendingdirections of the neurites can be controlled. The neuronal communicationcan be propagated.

When the culture medium is implanted into a wound of a human body ormammal body, neurites extending from a neuron cell will branch along theaxial directions of the carbon nanotube wires until the neurites connectwith ends or edges of the wound. Thus, the wound can be healed, and theneuronal communication can be regenerated.

Example

The method for culturing neural cells using the culture medium 10includes the following steps.

A culture medium is provided. The culture medium consists of a circularsheet-shaped plastic substrate and a carbon nanotube structure locatedon the circular sheet-shaped plastic substrate. The carbon nanotubestructure is formed by a single carbon nanotube film. The carbonnanotube structure includes carbon nanotube wires with diameters morethan 1 micrometer, and less than or equal to 10 micrometers. Thedistance between adjacent carbon nanotube wires is greater than or equalto 30 micrometers, and less than or equal to 60 micrometers, especiallythe distance is about 50 micromenters.

The culture medium is fixed on the bottom of a plastic culture vessel.The circular sheet-shaped plastic substrate contacts the bottom of theplastic culture vessel. The plastic culture vessel with the culturemedium fixed therein is put into an ultraviolet light sterilizing box.The culture medium and the plastic culture vessel are irradiated withultraviolet light for about 2.5 hours to eliminate microorganisms, suchas bacteria. The sterilized carbon nanotube structure is then treatedwith a poly-D-lysine solution having a concentration of about 20 μg/ml,until a surface of the carbon nanotube structure is completely coveredby the poly-D-lysine solution. The carbon nanotube structure is soakedin the poly-D-lysine solution for about 20 hours. The poly-D-lysinesolution on the surface of the carbon nanotube structure is removed byrinsing the carbon nanotube structure with sterilized deionized water.The surface of the carbon nanotube structure treated with poly-D-lysinesolution is polarized and becomes a polar surface.

Under sterile conditions, a hippocampal neuron solution is dropped onthe polar surface of the carbon nanotube structure until the hippocampalneuron solution substantially covers the polar surface. The hippocampalneuron cells in the hippocampal neuron solution are absorbed on thecircular sheet-shaped plastic substrate.

The culture vessel with the hippocampal neuron cells on the culturemedium is put in the incubator with a CO₂ concentration of about 5% anda temperature of about 37° C. for about 7 days. The hippocampal neuroncells are incubated in the incubator. During the optimal culture period,the feeding solution is replaced timely. Referring to FIG. 4, a numberof neurites from a cell body of the individual hippocampal neuron cellsare absorbed on the polar surface and branch along the carbon nanotubewires in the carbon nanotube structure. The neurites connect withadjacent hippocampal neuron cells to form a neuronal network.

Referring to FIG. 9, one embodiment of a culture medium 20 consists of acarbon nanotube structure 22 and the substrate 14 for loading the carbonnanotube structure 22. The carbon nanotube structure 22 includes twolayers of carbon nanotube films. Each carbon nanotube film includes anumber of carbon nanotube wires 123 extending substantially along a samedirection. The carbon nanotube wires 123 in the two carbon nanotubefilms are substantially perpendicular to each other. As such a netstructure is formed in the carbon nanotube structure 22. The distance ofthe adjacent carbon nanotube wires 123 in each carbon nanotube film aregreater than or equal to 30 micrometers, and less than or equal to 80micrometers. A diameter of each carbon nanotube wire 123 is larger than1 micrometer, and less than or equal to 10 micrometers. The substrate 14is a circular sheet-shaped plastic.

In one embodiment, a method for making the culture medium 20 includes:providing an original carbon nanotube structure consisting of two drawncarbon nanotube films, the carbon nanotubes in the two drawn carbonnanotube film define angles of about 90 degrees; fixing the originalcarbon nanotube structure on a frame and suspending the original carbonnanotube structure; spraying alcohol from a sprayer onto the originalcarbon nanotube structure to soak the original carbon nanotubestructure, wherein during the spraying process, alcohol is atomized intoseveral micrometer diameter drops and is taken out by a weak airflow andfalling on the drawn carbon nanotube film; evaporating the soakedoriginal carbon nanotube structure to converge the carbon nanotubes ineach drawn carbon nanotube film into carbon nanotube wires 123, therebyforming the carbon nanotube structure 22; forming the carbon nanotubestructure 22 into a circular shape, and placing it on a circularsheet-shaped plastic substrate 14; dropping alcohol on the circularcarbon nanotube structure 22; and evaporating the alcohol to attach thecircular carbon nanotube structure 22 to the circular sheet-shapedplastic substrate 14 tightly.

In one embodiment, a method for culturing neural cells using the culturemedium 20 is similar to the method for culturing neural cells using theculture medium 10. Referring to FIG. 10, the carbon nanotube wires inthe carbon nanotube structure 22 define a number of grids. The neuritesextending from the neuron cells are absorbed on the grids of the carbonnanotube structure 22. The neurites substantially grow along the grids.The neurites can be formed into a folded linear structure guided bygrids defined by the carbon nanotube wires.

Referring to FIG. 11, one embodiment of a culture medium 30 includes asubstrate 34, a carbon nanotube structure 12 stacked on the substrate34, and a container 36. The container 36 is used to load the substrate34 and the carbon nanotube structure 12, and can receive liquid agents.The container 36 can be a culture vessel or a watch glass. The container36 can be made of plastic, such as polystyrene. The substrate 34 can bea sheet-shaped structure. The substrate 34 is located between the carbonnanotube structure 12 and a bottom surface of the container 36. In oneembodiment, the substrate 34 is a circular sheet-shaped polystyrene, thesubstrate 34 is fixed in the container 36 by an adhesive. The container36 can grow neural cells using the culture medium 30. The culture medium30 including the container 36 is convenient for storing andtransporting.

In one embodiment, a method for making the culture medium 30 is similarto the method for making the culture medium 10. The method for makingthe culture medium 30 further includes step S340 after step S130 of themethod for making the culture medium 10. The step S340 can fix thesubstrate with the carbon nanotube thereon in the container.

In one embodiment, the step S340 includes: providing a container 36coated with an adhesive on the bottom of the container 36; placing thesubstrate 34 on the adhesive, with the substrate 34 located between theadhesive and the carbon nanotube structure 12; and heating the container36 with the substrate 34 and the carbon nanotube structure 12 in avacuum to remove toxic substances in the adhesive. During the heatingprocess, the container 36, the substrate 34, and the carbon nanotubestructure 12 will not deform or melt. A heating temperature can be lessthan or equal to 95 centigrade degrees. The heating time can bedetermined by the material of the container 36 and the substrate 34. Inone embodiment, the heating temperature is larger than or equal to 80centigrade degrees, and less than or equal to 95 centigrade degrees. Theheating time is about 30 minutes.

In the step S340, the substrate 34 is tightly fixed in the container 36,and air bubbles between the carbon nanotube structure 12 and thesubstrate 34 can be removed by heating such that the carbon nanotubestructure 12 can be tightly attached to the substrate 34.

A method for culturing neural cells using the culture medium 30 issubstantially the same with the method for culturing neural cells usingthe culture medium 10.

Referring to FIG. 12, one embodiment of a nerve graft 100 includes aculture medium 110 and a neural network 130 absorbed on the culturemedium 110. The culture medium 110 includes a biological substrate 114and a carbon nanotube structure 12 located on the biological substrate114. A surface of the carbon nanotube structure 12 is polarized to formthe polar surface. The polar surface has a different surface charge fromthe neural network 130. Thus, the neural network 130 is absorbed on theculture medium 110. A material of the biological substrate 114 can besilicone, a biodegradable material, or biocompatible materials. Theshape of the biological substrate 114 is not limited, and can be asheet-shaped structure.

The carbon nanotube wires 123 are arranged in a certain order. Thecarbon nanotube wires 123 can be parallel to each other or crossed witheach other forming a patterned structure. The neural network 130includes a number of neural cells 132. The neural cells 132 are absorbedon the biological substrate 114. Each neural cell 132 includes a neuralcell body 136 and at least one neurite 134 extending from the neuralcell body 136. The neural cell body 136 is absorbed on the biologicalsubstrate 114. The at least one neurite 134 is substantially absorbed onthe polar surface of the carbon nanotube structure, and substantiallybranches along the carbon nanotube wires 123. Each neurite 134 can be ina linear shape, folded linear shape, quadrangular shape, sector, orother curved shape. The shape of the neurite 134 can be controlled bythe carbon nanotube wires 123 in the carbon nanotube structure 12. Theat least one neurite 134 can be patterned. The arrangement of the carbonnanotube wires 123 in the carbon nanotube structure 12 can be determinedby the shape of a wound. The extending direction of the neurite 134 canfollow substantially along the carbon nanotube wires 123, and connectwith edges of the wound part. The wound can then communicate with andconnect to each other, thereby healing quickly.

In one embodiment, the nerve graft 100 includes a sheet-shaped siliconesubstrate, a single carbon nanotube film located on the siliconesubstrate, and a hippocampal neural network absorbed on the siliconsubstrate. The carbon nanotube wires in the carbon nanotube film extendsubstantially along a single direction and are juxtaposed. Thehippocampal neural network includes a number of hippocampal neuralcells. Each hippocampal neural cell branches a number of neurites. Theneurites extend substantially along the carbon nanotube wires to formlinear neurites.

It is to be understood that the above-described embodiments are intendedto illustrate rather than limit the disclosure. Variations may be madeto the embodiments without departing from the spirit of the disclosureas claimed. The above-described embodiments are intended to illustratethe scope of the disclosure and not restricted to the scope of thedisclosure.

It is also to be understood that the above description and the claimsdrawn to a method may include some indication in reference to certainsteps. However, the indication used is only to be viewed foridentification purposes and not as a suggestion as to an order for thesteps.

1. A culture medium for culturing neural cells, each neural cellcomprising a neural cell body and at least one neurite branched from theneural cell body, the culture medium comprising: a substrate; and acarbon nanotube structure located on the substrate, the carbon nanotubestructure comprising a plurality of carbon nanotube wires spaced apartfrom each other, wherein a distance between adjacent carbon nanotubewires is greater than or equal to a diameter of the neural cell body,and the plurality of carbon nanotube wires are capable of guidingextending directions of the neurites.
 2. The culture medium of claim 1,wherein a surface of the carbon nanotube structure is polarized into apolar surface, the polar surface is configured to absorb the neuralcells, and a surface charge polarity of the polar surface is differentfrom a surface change polarity of the neural cells.
 3. The culturemedium of claim 1, wherein a diameter of each carbon nanotube wire islarger than or equal to 1 micrometer, and less than or equal to 10micrometers.
 4. The culture medium of claim 1, wherein the distance isgreater than or equal to 20 micrometers, and less than or equal to 100micrometers.
 5. The culture medium of claim 1, wherein each carbonnanotube wire comprises a plurality of carbon nanotubes substantiallyparallel to each other and oriented along an axial direction of thecarbon nanotube wire, and adjacent carbon nanotubes are combined by vander Waals force.
 6. The culture medium of claim 5, wherein the pluralityof carbon nanotubes in each carbon nanotube wire are joined end to endwith each other along the axial direction of the carbon nanotube wire.7. The culture medium of claim 1, wherein each carbon nanotube wirecomprises a plurality of carbon nanotubes extending spirally along anaxial direction of the carbon nanotube wire.
 8. The culture medium ofclaim 1, wherein the carbon nanotube structure comprises at least onecarbon nanotube film comprising a plurality of substantially parallelcarbon nanotube wires and at least one carbon nanotube located betweenadjacent carbon nanotube wires by van der Waals force.
 9. The culturemedium of claim 8, wherein the carbon nanotube structure comprises aplurality of carbon nanotube films, and the carbon nanotube wires inadjacent carbon nanotube films define an angle.
 10. The culture mediumof claim 1, wherein a material of the substrate is selected from thegroup consisting of plastic, silicone, biodegradable material, andcarbon nanotube.
 11. The culture medium of claim 1, wherein thesubstrate is a sheet-shaped structure.
 12. The culture medium of claim11, further comprising a container comprising a bottom, wherein thesubstrate is fixed between the bottom of the container and the carbonnanotube structure.
 13. The culture medium of claim 12, wherein thecontainer is a culture vessel or a watch glass.
 14. The culture mediumof claim 12, further comprising an adhesive layer capable of adheringthe substrate to the bottom of the container.
 15. A culture medium forculturing neural cells, each neural cell comprising a neural cell bodyand at least one neurite branched from the neural cell body, the culturemedium comprising: a substrate; and a carbon nanotube structure locatedon the substrate, the carbon nanotube structure comprising a pluralityof carbon nanotube wires capable of guiding extending directions of theneurites, wherein the plurality of carbon nanotube wires are crossedwith each other to define a plurality of pores, and an effectivediameter of each pore is greater than or equal to a diameter of theneural cell body.
 16. A culture medium for culturing neural cells, eachneural cell comprising a neural cell body and at least one neuritebranched from the neural cell body, the culture medium comprising: asubstrate; and a carbon nanotube structure located on the substrate, thecarbon nanotube structure comprising at least one carbon nanotube filmcomprising a plurality of carbon nanotube wires spaced apart from eachother, wherein at least one carbon nanotube is combined with adjacentcarbon nanotube wires, a distance between adjacent carbon nanotube wiresis greater than or equal to a diameter of the neural cell body, and theplurality of carbon nanotube wires are capable of guiding extendingdirections of the neurites.
 17. The culture medium of claim 16, whereineach carbon nanotube wire comprises a plurality of carbon nanotubesorderly arranged.
 18. The culture medium of claim 16, wherein thesubstrate is a sheet-shaped structure.
 19. The culture medium of claim11, further comprising a container comprising a bottom, wherein thesubstrate is fixed between the bottom and the carbon nanotube structure.20. The culture medium of claim 12, wherein the container is a culturevessel or a watch glass.